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</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="jam.language"></a><a class="link" href="language.html" title="Language">Language</a>
</h2></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="language.html#jam.language.lexical">Lexical Features</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.target">Targets</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.rules">Rules</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.flow_of_control">Flow-of-Control</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.variables">Variables</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.modules">Modules</a></span></dt>
</dl></div>
<p>
      <code class="literal">BJam</code> has an interpreted, procedural language. Statements
      in <code class="literal">bjam</code> are rule (procedure) definitions, rule invocations,
      flow-of-control structures, variable assignments, and sundry language support.
    </p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="jam.language.lexical"></a><a class="link" href="language.html#jam.language.lexical" title="Lexical Features">Lexical Features</a>
</h3></div></div></div>
<p>
        <code class="literal">BJam</code> treats its input files as whitespace-separated tokens,
        with two exceptions: double quotes (") can enclose whitespace to embed
        it into a token, and everything between the matching curly braces ({}) in
        the definition of a rule action is treated as a single string. A backslash
        (\) can escape a double quote, or any single whitespace character.
      </p>
<p>
        <code class="literal">BJam</code> requires whitespace (blanks, tabs, or newlines) to
        surround all tokens, including the colon (:) and semicolon (;) tokens.
      </p>
<p>
        <code class="literal">BJam</code> keywords (an mentioned in this document) are reserved
        and generally must be quoted with double quotes (") to be used as arbitrary
        tokens, such as variable or target names.
      </p>
<p>
        Comments start with the <code class="literal">#</code> character and extend until the
        end of line.
      </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="jam.language.target"></a><a class="link" href="language.html#jam.language.target" title="Targets">Targets</a>
</h3></div></div></div>
<div class="toc"><dl><dt><span class="section"><a href="language.html#jam.language.target.binding_detection">Binding Detection</a></span></dt></dl></div>
<p>
        The essential <code class="literal">bjam</code> data entity is a target. Build targets
        are files to be updated. Source targets are the files used in updating built
        targets. Built targets and source targets are collectively referred to as
        file targets, and frequently built targets are source targets for other built
        targets. Pseudotargets are symbols which represent dependencies on other
        targets, but which are not themselves associated with any real file.
      </p>
<p>
        A file target's identifier is generally the file's name, which can be absolutely
        rooted, relative to the directory of <code class="literal">bjam</code>'s invocation,
        or simply local (no directory). Most often it is the last case, and the actual
        file path is bound using the <code class="literal">$(SEARCH)</code> and <code class="literal">$(LOCATE)</code>
        special variables. See <a class="link" href="language.html#jam.language.variables.builtins.search" title="SEARCH and LOCATE">SEARCH
        and LOCATE Variables</a> below. A local filename is optionally qualified
        with grist, a string value used to assure uniqueness. A file target with
        an identifier of the form <span class="emphasis"><em>file(member)</em></span> is a library
        member (usually an <code class="literal">ar</code>(1) archive on Unix).
      </p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="jam.language.target.binding_detection"></a><a class="link" href="language.html#jam.language.target.binding_detection" title="Binding Detection">Binding Detection</a>
</h4></div></div></div>
<p>
          Whenever a target is bound to a location in the filesystem, Boost Jam will
          look for a variable called <code class="literal">BINDRULE</code> (first "on"
          the target being bound, then in the global module). If non-empty, =$(BINDRULE[1])=
          names a rule which is called with the name of the target and the path it
          is being bound to. The signature of the rule named by =$(BINDRULE[1])=
          should match the following:
        </p>
<pre class="programlisting">rule <span class="emphasis"><em>bind-rule</em></span> ( <span class="emphasis"><em>target</em></span> : <span class="emphasis"><em>path</em></span> )
</pre>
<p>
          This facility is useful for correct header file scanning, since many compilers
          will search for <code class="computeroutput"><span class="preprocessor">#include</span></code>
          files first in the directory containing the file doing the <code class="computeroutput"><span class="preprocessor">#include</span></code> directive. <code class="literal">$(BINDRULE)</code>
          can be used to make a record of that directory.
        </p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="jam.language.rules"></a><a class="link" href="language.html#jam.language.rules" title="Rules">Rules</a>
</h3></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="language.html#jam.language.rules.action_modifiers">Action Modifiers</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.rules.argument_lists">Argument lists</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.rules.builtins">Built-in Rules</a></span></dt>
</dl></div>
<p>
        The basic <code class="literal">bjam</code> language entity is called a rule. A rule
        is defined in two parts: the procedure and the actions. The procedure is
        a body of jam statements to be run when the rule is invoked; the actions
        are the OS shell commands to execute when updating the built targets of the
        rule.
      </p>
<p>
        Rules can return values, which can be expanded into a list with "[
        <span class="emphasis"><em>rule</em></span> <span class="emphasis"><em>args</em></span> ... ]". A rule's
        value is the value of its last statement, though only the following statements
        have values: 'if' (value of the leg chosen), 'switch' (value of the case
        chosen), set (value of the resulting variable), and 'return' (value of its
        arguments). Note that 'return' doesn't actually cause a return, i.e., is
        a no-op unless it is the last statement of the last block executed within
        rule body.
      </p>
<p>
        The <code class="literal">bjam</code> statements for defining and invoking rules are
        as follows:
      </p>
<p>
        Define a rule's procedure, replacing any previous definition.
      </p>
<pre class="programlisting">rule <span class="emphasis"><em>rulename</em></span> { <span class="emphasis"><em>statements</em></span> }
</pre>
<p>
        Define a rule's updating actions, replacing any previous definition.
      </p>
<pre class="programlisting">actions [ <span class="emphasis"><em>modifiers</em></span> ] <span class="emphasis"><em>rulename</em></span> { <span class="emphasis"><em>commands</em></span> }
</pre>
<p>
        Invoke a rule.
      </p>
<pre class="programlisting"><span class="emphasis"><em>rulename</em></span> <span class="emphasis"><em>field1</em></span> : <span class="emphasis"><em>field2</em></span> : <span class="emphasis"><em>...</em></span> : <span class="emphasis"><em>fieldN</em></span> ;
</pre>
<p>
        Invoke a rule under the influence of target's specific variables..
      </p>
<pre class="programlisting">on <span class="emphasis"><em>target</em></span> <span class="emphasis"><em>rulename</em></span> <span class="emphasis"><em>field1</em></span> : <span class="emphasis"><em>field2</em></span> : <span class="emphasis"><em>...</em></span> : <span class="emphasis"><em>fieldN</em></span> ;
</pre>
<p>
        Used as an argument, expands to the return value of the rule invoked.
      </p>
<pre class="programlisting">[ <span class="emphasis"><em>rulename</em></span> <span class="emphasis"><em>field1</em></span> : <span class="emphasis"><em>field2</em></span> : <span class="emphasis"><em>...</em></span> : <span class="emphasis"><em>fieldN</em></span> ]
[ on <span class="emphasis"><em>target</em></span> <span class="emphasis"><em>rulename</em></span> <span class="emphasis"><em>field1</em></span> : <span class="emphasis"><em>field2</em></span> : <span class="emphasis"><em>...</em></span> : <span class="emphasis"><em>fieldN</em></span> ]
</pre>
<p>
        A rule is invoked with values in <span class="emphasis"><em>field1</em></span> through <span class="emphasis"><em>fieldN</em></span>.
        They may be referenced in the procedure's statements as <code class="literal">$(1)</code>
        through <code class="literal">$(<span class="emphasis"><em>N</em></span>)</code> (9 max), and the first
        two only may be referenced in the action's <span class="emphasis"><em>commands</em></span>
        as <code class="literal">$(1)</code> and <code class="literal">$(2)</code>. <code class="literal">$(&lt;)</code>
        and <code class="literal">$(&gt;)</code> are synonymous with <code class="literal">$(1)</code>
        and <code class="literal">$(2)</code>.
      </p>
<p>
        Rules fall into two categories: updating rules (with actions), and pure procedure
        rules (without actions). Updating rules treat arguments <code class="literal">$(1)</code>
        and <code class="literal">$(2)</code> as built targets and sources, respectively, while
        pure procedure rules can take arbitrary arguments.
      </p>
<p>
        When an updating rule is invoked, its updating actions are added to those
        associated with its built targets (<code class="literal">$(1)</code>) before the rule's
        procedure is run. Later, to build the targets in the updating phase, <span class="emphasis"><em>commands</em></span>
        are passed to the OS command shell, with <code class="literal">$(1)</code> and <code class="literal">$(2)</code>
        replaced by bound versions of the target names. See Binding above.
      </p>
<p>
        Rule invocation may be indirected through a variable:
      </p>
<pre class="programlisting">$(<span class="emphasis"><em>var</em></span>) <span class="emphasis"><em>field1</em></span> : <span class="emphasis"><em>field2</em></span> : <span class="emphasis"><em>...</em></span> : <span class="emphasis"><em>fieldN</em></span> ;

on <span class="emphasis"><em>target</em></span> $(<span class="emphasis"><em>var</em></span>) <span class="emphasis"><em>field1</em></span> : <span class="emphasis"><em>field2</em></span> : <span class="emphasis"><em>...</em></span> : <span class="emphasis"><em>fieldN</em></span> ;

[ $(<span class="emphasis"><em>var</em></span>) <span class="emphasis"><em>field1</em></span> : <span class="emphasis"><em>field2</em></span> : <span class="emphasis"><em>...</em></span> : <span class="emphasis"><em>fieldN</em></span> ]
[ on <span class="emphasis"><em>target</em></span> $(<span class="emphasis"><em>var</em></span>) <span class="emphasis"><em>field1</em></span> : <span class="emphasis"><em>field2</em></span> : <span class="emphasis"><em>...</em></span> : <span class="emphasis"><em>fieldN</em></span> ]
</pre>
<p>
        The variable's value names the rule (or rules) to be invoked. A rule is invoked
        for each element in the list of <code class="literal">$(<span class="emphasis"><em>var</em></span>)</code>'s
        values. The fields <code class="literal"><span class="emphasis"><em>field1</em></span> : <span class="emphasis"><em>field2</em></span>
        : <span class="emphasis"><em>...</em></span></code> are passed as arguments for each invokation.
        For the [ ... ] forms, the return value is the concatenation of the return
        values for all of the invocations.
      </p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="jam.language.rules.action_modifiers"></a><a class="link" href="language.html#jam.language.rules.action_modifiers" title="Action Modifiers">Action Modifiers</a>
</h4></div></div></div>
<p>
          The following action modifiers are understood:
        </p>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term"><code class="literal">actions bind <span class="emphasis"><em>vars</em></span></code></span></dt>
<dd><p>
                <code class="literal">$(<span class="emphasis"><em>vars</em></span>)</code> will be replaced
                with bound values.
              </p></dd>
<dt><span class="term"><code class="literal">actions existing</code></span></dt>
<dd><p>
                <code class="literal">$(&gt;)</code> includes only source targets currently
                existing.
              </p></dd>
<dt><span class="term"><code class="literal">actions ignore</code></span></dt>
<dd><p>
                The return status of the commands is ignored.
              </p></dd>
<dt><span class="term"><code class="literal">actions piecemeal</code></span></dt>
<dd><p>
                commands are repeatedly invoked with a subset of <code class="literal">$(&gt;)</code>
                small enough to fit in the command buffer on this OS.
              </p></dd>
<dt><span class="term"><code class="literal">actions quietly</code></span></dt>
<dd><p>
                The action is not echoed to the standard output.
              </p></dd>
<dt><span class="term"><code class="literal">actions together</code></span></dt>
<dd><p>
                The <code class="literal">$(&gt;)</code> from multiple invocations of the same
                action on the same built target are glommed together.
              </p></dd>
<dt><span class="term"><code class="literal">actions updated</code></span></dt>
<dd><p>
                <code class="literal">$(&gt;)</code> includes only source targets themselves
                marked for updating.
              </p></dd>
</dl>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="jam.language.rules.argument_lists"></a><a class="link" href="language.html#jam.language.rules.argument_lists" title="Argument lists">Argument lists</a>
</h4></div></div></div>
<p>
          You can describe the arguments accepted by a rule, and refer to them by
          name within the rule. For example, the following prints "I'm sorry,
          Dave" to the console:
        </p>
<pre class="programlisting">rule report ( pronoun index ? : state : names + )
{
    local he.suffix she.suffix it.suffix = s ;
    local I.suffix = m ;
    local they.suffix you.suffix = re ;
    ECHO $(pronoun)'$($(pronoun).suffix) $(state), $(names[$(index)]) ;
}
report I 2 : sorry : Joe Dave Pete ;
</pre>
<p>
          Each name in a list of formal arguments (separated by "<code class="literal">:</code>"
          in the rule declaration) is bound to a single element of the corresponding
          actual argument unless followed by one of these modifiers:
        </p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                  <p>
                    Symbol
                  </p>
                </th>
<th>
                  <p>
                    Semantics of preceding symbol
                  </p>
                </th>
</tr></thead>
<tbody>
<tr>
<td>
                  <p>
                    <code class="literal">?</code>
                  </p>
                </td>
<td>
                  <p>
                    optional
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p>
                    <code class="literal">*</code>
                  </p>
                </td>
<td>
                  <p>
                    Bind to zero or more unbound elements of the actual argument.
                    When <code class="literal">*</code> appears where an argument name is expected,
                    any number of additional arguments are accepted. This feature
                    can be used to implement "varargs" rules.
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p>
                    <code class="literal">+</code>
                  </p>
                </td>
<td>
                  <p>
                    Bind to one or more unbound elements of the actual argument.
                  </p>
                </td>
</tr>
</tbody>
</table></div>
<p>
          The actual and formal arguments are checked for inconsistencies, which
          cause Jam to exit with an error code:
        </p>
<pre class="programlisting">### argument error
# rule report ( pronoun index ?  : state  : names + )
# called with: ( I 2 foo  : sorry  : Joe Dave Pete )
# extra argument foo
### argument error
# rule report ( pronoun index ?  : state  : names + )
# called with: ( I 2  : sorry )
# missing argument names
</pre>
<p>
          If you omit the list of formal arguments, all checking is bypassed as in
          "classic" Jam. Argument lists drastically improve the reliability
          and readability of your rules, however, and are <span class="bold"><strong>strongly
          recommended</strong></span> for any new Jam code you write.
        </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="jam.language.rules.builtins"></a><a class="link" href="language.html#jam.language.rules.builtins" title="Built-in Rules">Built-in Rules</a>
</h4></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="language.html#jam.language.rules.builtins.dependency_building">Dependency
          Building</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.rules.builtins.modifying_binding">Modifying
          Binding</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.rules.builtins.utility">Utility</a></span></dt>
</dl></div>
<p>
          <code class="literal">BJam</code> has a growing set of built-in rules, all of which
          are pure procedure rules without updating actions. They are in three groups:
          the first builds the dependency graph; the second modifies it; and the
          third are just utility rules.
        </p>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="jam.language.rules.builtins.dependency_building"></a><a class="link" href="language.html#jam.language.rules.builtins.dependency_building" title="Dependency Building">Dependency
          Building</a>
</h5></div></div></div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.dependency_building._depends__"></a><a class="link" href="language.html#jam.language.rules.builtins.dependency_building._depends__" title="DEPENDS"><code class="literal">DEPENDS</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule DEPENDS ( <span class="emphasis"><em>targets1</em></span> * : <span class="emphasis"><em>targets2</em></span> * )
</pre>
<p>
              Builds a direct dependency: makes each of <span class="emphasis"><em>targets1</em></span>
              depend on each of <span class="emphasis"><em>targets2</em></span>. Generally, <span class="emphasis"><em>targets1</em></span>
              will be rebuilt if <span class="emphasis"><em>targets2</em></span> are themselves rebuilt
              or are newer than <span class="emphasis"><em>targets1</em></span>.
            </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.dependency_building._includes__"></a><a class="link" href="language.html#jam.language.rules.builtins.dependency_building._includes__" title="INCLUDES"><code class="literal">INCLUDES</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule INCLUDES ( <span class="emphasis"><em>targets1</em></span> * : <span class="emphasis"><em>targets2</em></span> * )
</pre>
<p>
              Builds a sibling dependency: makes any target that depends on any of
              <span class="emphasis"><em>targets1</em></span> also depend on each of <span class="emphasis"><em>targets2</em></span>.
              This reflects the dependencies that arise when one source file includes
              another: the object built from the source file depends both on the
              original and included source file, but the two sources files don't
              depend on each other. For example:
            </p>
<pre class="programlisting">DEPENDS foo.o : foo.c ;
INCLUDES foo.c : foo.h ;
</pre>
<p>
              "<code class="literal">foo.o</code>" depends on "<code class="literal">foo.c</code>"
              and "<code class="literal">foo.h</code>" in this example.
            </p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="jam.language.rules.builtins.modifying_binding"></a><a class="link" href="language.html#jam.language.rules.builtins.modifying_binding" title="Modifying Binding">Modifying
          Binding</a>
</h5></div></div></div>
<p>
            The six rules <code class="literal">ALWAYS</code>, <code class="literal">LEAVES</code>,
            <code class="literal">NOCARE</code>, <code class="literal">NOTFILE</code>, <code class="literal">NOUPDATE</code>,
            and <code class="literal">TEMPORARY</code> modify the dependency graph so that
            <code class="literal">bjam</code> treats the targets differently during its target
            binding phase. See Binding above. Normally, <code class="literal">bjam</code> updates
            a target if it is missing, if its filesystem modification time is older
            than any of its dependencies (recursively), or if any of its dependencies
            are being updated. This basic behavior can be changed by invoking the
            following rules:
          </p>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.modifying_binding._always__"></a><a class="link" href="language.html#jam.language.rules.builtins.modifying_binding._always__" title="ALWAYS"><code class="literal">ALWAYS</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule ALWAYS ( <span class="emphasis"><em>targets</em></span> * )
</pre>
<p>
              Causes <span class="emphasis"><em>targets</em></span> to be rebuilt regardless of whether
              they are up-to-date (they must still be in the dependency graph). This
              is used for the clean and uninstall targets, as they have no dependencies
              and would otherwise appear never to need building. It is best applied
              to targets that are also <code class="literal">NOTFILE</code> targets, but it
              can also be used to force a real file to be updated as well.
            </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.modifying_binding._leaves__"></a><a class="link" href="language.html#jam.language.rules.builtins.modifying_binding._leaves__" title="LEAVES"><code class="literal">LEAVES</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule LEAVES ( <span class="emphasis"><em>targets</em></span> * )
</pre>
<p>
              Makes each of <span class="emphasis"><em>targets</em></span> depend only on its leaf
              sources, and not on any intermediate targets. This makes it immune
              to its dependencies being updated, as the "leaf" dependencies
              are those without their own dependencies and without updating actions.
              This allows a target to be updated only if original source files change.
            </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.modifying_binding._nocare__"></a><a class="link" href="language.html#jam.language.rules.builtins.modifying_binding._nocare__" title="NOCARE"><code class="literal">NOCARE</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule NOCARE ( <span class="emphasis"><em>targets</em></span> * )
</pre>
<p>
              Causes <code class="literal">bjam</code> to ignore <span class="emphasis"><em>targets</em></span>
              that neither can be found nor have updating actions to build them.
              Normally for such targets <code class="literal">bjam</code> issues a warning
              and then skips other targets that depend on these missing targets.
              The <code class="literal">HdrRule</code> in <code class="literal">Jambase</code> uses
              <code class="literal">NOCARE</code> on the header file names found during header
              file scanning, to let <code class="literal">bjam</code> know that the included
              files may not exist. For example, if an <code class="computeroutput"><span class="preprocessor">#include</span></code>
              is within an <code class="computeroutput"><span class="preprocessor">#ifdef</span></code>,
              the included file may not actually be around.
            </p>
<div class="warning"><table border="0" summary="Warning">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../doc/src/images/warning.png"></td>
<th align="left">Warning</th>
</tr>
<tr><td align="left" valign="top"><p>
                For targets with build actions: if their build actions exit with
                a nonzero return code, dependent targets will still be built.
              </p></td></tr>
</table></div>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.modifying_binding._notfile__"></a><a class="link" href="language.html#jam.language.rules.builtins.modifying_binding._notfile__" title="NOTFILE"><code class="literal">NOTFILE</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule NOTFILE ( <span class="emphasis"><em>targets</em></span> * )
</pre>
<p>
              Marks <span class="emphasis"><em>targets</em></span> as pseudotargets and not real files.
              No timestamp is checked, and so the actions on such a target are only
              executed if the target's dependencies are updated, or if the target
              is also marked with <code class="literal">ALWAYS</code>. The default <code class="literal">bjam</code>
              target "<code class="literal">all</code>" is a pseudotarget. In <code class="literal">Jambase</code>,
              <code class="literal">NOTFILE</code> is used to define several addition convenient
              pseudotargets.
            </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.modifying_binding._noupdate__"></a><a class="link" href="language.html#jam.language.rules.builtins.modifying_binding._noupdate__" title="NOUPDATE"><code class="literal">NOUPDATE</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule NOUPDATE ( <span class="emphasis"><em>targets</em></span> * )
</pre>
<p>
              Causes the timestamps on <span class="emphasis"><em>targets</em></span> to be ignored.
              This has two effects: first, once the target has been created it will
              never be updated; second, manually updating target will not cause other
              targets to be updated. In <code class="literal">Jambase</code>, for example,
              this rule is applied to directories by the <code class="literal">MkDir</code>
              rule, because <code class="literal">MkDir</code> only cares that the target directory
              exists, not when it has last been updated.
            </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.modifying_binding._temporary__"></a><a class="link" href="language.html#jam.language.rules.builtins.modifying_binding._temporary__" title="TEMPORARY"><code class="literal">TEMPORARY</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule TEMPORARY ( <span class="emphasis"><em>targets</em></span> * )
</pre>
<p>
              Marks <span class="emphasis"><em>targets</em></span> as temporary, allowing them to be
              removed after other targets that depend upon them have been updated.
              If a <code class="literal">TEMPORARY</code> target is missing, <code class="literal">bjam</code>
              uses the timestamp of the target's parent. <code class="literal">Jambase</code>
              uses <code class="literal">TEMPORARY</code> to mark object files that are archived
              in a library after they are built, so that they can be deleted after
              they are archived.
            </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.modifying_binding._fail_expected__"></a><a class="link" href="language.html#jam.language.rules.builtins.modifying_binding._fail_expected__" title="FAIL_EXPECTED"><code class="literal">FAIL_EXPECTED</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule FAIL_EXPECTED ( <span class="emphasis"><em>targets</em></span> * )
</pre>
<p>
              For handling targets whose build actions are expected to fail (e.g.
              when testing that assertions or compile-time type checking work properly),
              Boost Jam supplies the <code class="literal">FAIL_EXPECTED</code> rule in the
              same style as <code class="literal">NOCARE</code>, et. al. During target updating,
              the return code of the build actions for arguments to <code class="literal">FAIL_EXPECTED</code>
              is inverted: if it fails, building of dependent targets continues as
              though it succeeded. If it succeeds, dependent targets are skipped.
            </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.modifying_binding._rmold__"></a><a class="link" href="language.html#jam.language.rules.builtins.modifying_binding._rmold__" title="RMOLD"><code class="literal">RMOLD</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule RMOLD ( <span class="emphasis"><em>targets</em></span> * )
</pre>
<p>
              <code class="literal">BJam</code> removes any target files that may exist on
              disk when the rule used to build those targets fails. However, targets
              whose dependencies fail to build are not removed by default. The <code class="literal">RMOLD</code>
              rule causes its arguments to be removed if any of their dependencies
              fail to build.
            </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.modifying_binding._isfile__"></a><a class="link" href="language.html#jam.language.rules.builtins.modifying_binding._isfile__" title="ISFILE"><code class="literal">ISFILE</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule ISFILE ( <span class="emphasis"><em>targets</em></span> * )
</pre>
<p>
              <code class="literal">ISFILE</code> marks targets as required to be files. This
              changes the way <code class="literal">bjam</code> searches for the target such
              that it ignores mathes for file system items that are not file, like
              directories. This makes it possible to avoid <code class="computeroutput"><span class="preprocessor">#include</span>
              <span class="string">"exception"</span></code> matching
              if one happens to have a directory named exception in the header search
              path.
            </p>
<div class="warning"><table border="0" summary="Warning">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../doc/src/images/warning.png"></td>
<th align="left">Warning</th>
</tr>
<tr><td align="left" valign="top"><p>
                This is currently not fully implemented.
              </p></td></tr>
</table></div>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="jam.language.rules.builtins.utility"></a><a class="link" href="language.html#jam.language.rules.builtins.utility" title="Utility">Utility</a>
</h5></div></div></div>
<p>
            The two rules <code class="literal">ECHO</code> and <code class="literal">EXIT</code> are
            utility rules, used only in <code class="literal">bjam</code>'s parsing phase.
          </p>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.utility._echo__"></a><a class="link" href="language.html#jam.language.rules.builtins.utility._echo__" title="ECHO"><code class="literal">ECHO</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule ECHO ( <span class="emphasis"><em>args</em></span> * )
</pre>
<p>
              Blurts out the message <span class="emphasis"><em>args</em></span> to stdout.
            </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.utility._exit__"></a><a class="link" href="language.html#jam.language.rules.builtins.utility._exit__" title="EXIT"><code class="literal">EXIT</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule EXIT ( <span class="emphasis"><em>message</em></span> * : <span class="emphasis"><em>result-value</em></span> ? )
</pre>
<p>
              Blurts out the <span class="emphasis"><em>message</em></span> to stdout and then exits
              with a failure status if no <span class="emphasis"><em>result-value</em></span> is given,
              otherwise it exits with the given <span class="emphasis"><em>result-value</em></span>.
            </p>
<p>
              "<code class="literal">Echo</code>", "<code class="literal">echo</code>",
              "<code class="literal">Exit</code>", and "<code class="literal">exit</code>"
              are accepted as aliases for <code class="literal">ECHO</code> and <code class="literal">EXIT</code>,
              since it is hard to tell that these are built-in rules and not part
              of the language, like "<code class="literal">include</code>".
            </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.utility._glob__"></a><a class="link" href="language.html#jam.language.rules.builtins.utility._glob__" title="GLOB"><code class="literal">GLOB</code>
            </a>
</h6></div></div></div>
<p>
              The <code class="literal">GLOB</code> rule does filename globbing.
            </p>
<pre class="programlisting">rule GLOB ( <span class="emphasis"><em>directories</em></span> * : <span class="emphasis"><em>patterns</em></span> * : <span class="emphasis"><em>downcase-opt</em></span> ? )
</pre>
<p>
              Using the same wildcards as for the patterns in the switch statement.
              It is invoked by being used as an argument to a rule invocation inside
              of "=[ ]=". For example: "<code class="literal">FILES = [ GLOB dir1
              dir2 : *.c *.h ]</code>" sets <code class="literal">FILES</code> to the
              list of C source and header files in <code class="literal">dir1</code> and <code class="literal">dir2</code>.
              The resulting filenames are the full pathnames, including the directory,
              but the pattern is applied only to the file name without the directory.
            </p>
<p>
              If <span class="emphasis"><em>downcase-opt</em></span> is supplied, filenames are converted
              to all-lowercase before matching against the pattern; you can use this
              to do case-insensitive matching using lowercase patterns. The paths
              returned will still have mixed case if the OS supplies them. On Windows
              NT and Cygwin, filenames are always downcased before matching.
            </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.utility._match__"></a><a class="link" href="language.html#jam.language.rules.builtins.utility._match__" title="MATCH"><code class="literal">MATCH</code>
            </a>
</h6></div></div></div>
<p>
              The <code class="literal">MATCH</code> rule does pattern matching.
            </p>
<pre class="programlisting">rule MATCH ( <span class="emphasis"><em>regexps</em></span> + : <span class="emphasis"><em>list</em></span> * )
</pre>
<p>
              Matches the <code class="literal">egrep</code>(1) style regular expressions
              <span class="emphasis"><em>regexps</em></span> against the strings in <span class="emphasis"><em>list</em></span>.
              The result is the concatenation of matching <code class="literal">()</code> subexpressions
              for each string in <span class="emphasis"><em>list</em></span>, and for each regular
              expression in <span class="emphasis"><em>regexps</em></span>. Only useful within the
              "=[ ]=" construct, to change the result into a list.
            </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.utility._backtrace__"></a><a class="link" href="language.html#jam.language.rules.builtins.utility._backtrace__" title="BACKTRACE"><code class="literal">BACKTRACE</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule BACKTRACE ( )
</pre>
<p>
              Returns a list of quadruples: <span class="emphasis"><em>filename</em></span> <span class="emphasis"><em>line</em></span>
              <span class="emphasis"><em>module</em></span> <span class="emphasis"><em>rulename</em></span>..., describing
              each shallower level of the call stack. This rule can be used to generate
              useful diagnostic messages from Jam rules.
            </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.utility._update__"></a><a class="link" href="language.html#jam.language.rules.builtins.utility._update__" title="UPDATE"><code class="literal">UPDATE</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule UPDATE ( <span class="emphasis"><em>targets</em></span> * )
</pre>
<p>
              Classic jam treats any non-option element of command line as a name
              of target to be updated. This prevented more sophisticated handling
              of command line. This is now enabled again but with additional changes
              to the <code class="literal">UPDATE</code> rule to allow for the flexibility
              of changing the list of targets to update. The UPDATE rule has two
              effects:
            </p>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
                  It clears the list of targets to update, and
                </li>
<li class="listitem">
                  Causes the specified targets to be updated.
                </li>
</ol></div>
<p>
              If no target was specified with the <code class="literal">UPDATE</code> rule,
              no targets will be updated. To support changing of the update list
              in more useful ways, the rule also returns the targets previously in
              the update list. This makes it possible to add targets as such:
            </p>
<pre class="programlisting">local previous-updates = [ UPDATE ] ;
UPDATE $(previous-updates) a-new-target ;
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.utility._w32_getreg__"></a><a class="link" href="language.html#jam.language.rules.builtins.utility._w32_getreg__" title="W32_GETREG"><code class="literal">W32_GETREG</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule W32_GETREG ( <span class="emphasis"><em>path</em></span> : <span class="emphasis"><em>data</em></span> ? )
</pre>
<p>
              Defined only for win32 platform. It reads the registry of Windows.
              '<span class="emphasis"><em>path</em></span>' is the location of the information, and
              '<span class="emphasis"><em>data</em></span>' is the name of the value which we want
              to get. If '<span class="emphasis"><em>data</em></span>' is omitted, the default value
              of '<span class="emphasis"><em>path</em></span>' will be returned. The '<span class="emphasis"><em>path</em></span>'
              value must conform to MS key path format and must be prefixed with
              one of the predefined root keys. As usual,
            </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
                  '<code class="literal">HKLM</code>' is equivalent to '<code class="literal">HKEY_LOCAL_MACHINE</code>'.
                </li>
<li class="listitem">
                  '<code class="literal">HKCU</code>' is equivalent to '<code class="literal">HKEY_CURRENT_USER</code>'.
                </li>
<li class="listitem">
                  '<code class="literal">HKCR</code>' is equivalent to '<code class="literal">HKEY_CLASSES_ROOT</code>'.
                </li>
</ul></div>
<p>
              Other predefined root keys are not supported.
            </p>
<p>
              Currently supported data types : '<code class="literal">REG_DWORD</code>', '<code class="literal">REG_SZ</code>',
              '<code class="literal">REG_EXPAND_SZ</code>', '<code class="literal">REG_MULTI_SZ</code>'.
              The data with '<code class="literal">REG_DWORD</code>' type will be turned into
              a string, '<code class="literal">REG_MULTI_SZ</code>' into a list of strings,
              and for those with '<code class="literal">REG_EXPAND_SZ</code>' type environment
              variables in it will be replaced with their defined values. The data
              with '<code class="literal">REG_SZ</code>' type and other unsupported types will
              be put into a string without modification. If it can't receive the
              value of the data, it just return an empty list. For example,
            </p>
<pre class="programlisting">local PSDK-location =
  [ W32_GETREG HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\MicrosoftSDK\\Directories : "Install Dir" ] ;
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.utility._w32_getregnames__"></a><a class="link" href="language.html#jam.language.rules.builtins.utility._w32_getregnames__" title="W32_GETREGNAMES"><code class="literal">W32_GETREGNAMES</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule W32_GETREGNAMES ( <span class="emphasis"><em>path</em></span> : <span class="emphasis"><em>result-type</em></span> )
</pre>
<p>
              Defined only for win32 platform. It reads the registry of Windows.
              '<span class="emphasis"><em>path</em></span>' is the location of the information, and
              '<span class="emphasis"><em>result-type</em></span>' is either '<code class="literal">subkeys</code>'
              or '<code class="literal">values</code>'. For more information on '<span class="emphasis"><em>path</em></span>'
              format and constraints, please see <code class="literal">W32_GETREG</code>.
            </p>
<p>
              Depending on '<span class="emphasis"><em>result-type</em></span>', the rule returns one
              of the following:
            </p>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term"><code class="literal">subkeys</code></span></dt>
<dd><p>
                    Names of all direct subkeys of '<span class="emphasis"><em>path</em></span>'.
                  </p></dd>
<dt><span class="term"><code class="literal">values</code></span></dt>
<dd><p>
                    Names of values contained in registry key given by '<span class="emphasis"><em>path</em></span>'.
                    The "default" value of the key appears in the returned
                    list only if its value has been set in the registry.
                  </p></dd>
</dl>
</div>
<p>
              If '<span class="emphasis"><em>result-type</em></span>' is not recognized, or requested
              data cannot be retrieved, the rule returns an empty list. Example:
            </p>
<pre class="programlisting">local key = "HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\App Paths" ;
local subkeys = [ W32_GETREGNAMES "$(key)" : subkeys ] ;
for local subkey in $(subkeys)
{
    local values = [ W32_GETREGNAMES "$(key)\\$(subkey)" : values ] ;
    for local value in $(values)
    {
        local data = [ W32_GETREG "$(key)\\$(subkey)" : "$(value)" ] ;
        ECHO "Registry path: " $(key)\\$(subkey) ":" $(value) "=" $(data) ;
    }
}
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.utility._shell__"></a><a class="link" href="language.html#jam.language.rules.builtins.utility._shell__" title="SHELL"><code class="literal">SHELL</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule SHELL ( <span class="emphasis"><em>command</em></span> : * )
</pre>
<p>
              <code class="literal">SHELL</code> executes <span class="emphasis"><em>command</em></span>, and
              then returns the standard output of <span class="emphasis"><em>command</em></span>.
              <code class="literal">SHELL</code> only works on platforms with a <code class="literal">popen()</code>
              function in the C library. On platforms without a working <code class="literal">popen()</code>
              function, <code class="literal">SHELL</code> is implemented as a no-op. <code class="literal">SHELL</code>
              works on Unix, MacOS X, and most Windows compilers. <code class="literal">SHELL</code>
              is a no-op on Metrowerks compilers under Windows. There is a variable
              set of allowed options as additional arguments:
            </p>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term"><code class="literal">exit-status</code></span></dt>
<dd><p>
                    In addition to the output the result status of the executed command
                    is returned as a second element of the result.
                  </p></dd>
<dt><span class="term"><code class="literal">no-output</code></span></dt>
<dd><p>
                    Don't capture the output of the command. Instead an empty ("")
                    string value is returned in place of the output.
                  </p></dd>
</dl>
</div>
<p>
              Because the Perforce/Jambase defines a <code class="literal">SHELL</code> rule
              which hides the builtin rule, <code class="literal">COMMAND</code> can be used
              as an alias for <code class="literal">SHELL</code> in such a case.
            </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.utility._md5__"></a><a class="link" href="language.html#jam.language.rules.builtins.utility._md5__" title="MD5"><code class="literal">MD5</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule MD5 ( <span class="emphasis"><em>string</em></span> )
</pre>
<p>
              <code class="literal">MD5</code> computes the MD5 hash of the string passed as
              paramater and returns it.
            </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.utility._split_by_characters__"></a><a class="link" href="language.html#jam.language.rules.builtins.utility._split_by_characters__" title="SPLIT_BY_CHARACTERS"><code class="literal">SPLIT_BY_CHARACTERS</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule SPLIT_BY_CHARACTERS ( <span class="emphasis"><em>string</em></span> : <span class="emphasis"><em>delimiters</em></span> )
</pre>
<p>
              <code class="literal">SPLIT_BY_CHARACTERS</code> splits the specified <span class="emphasis"><em>string</em></span>
              on any delimiter character present in <span class="emphasis"><em>delimiters</em></span>
              and returns the resulting list.
            </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.utility._precious__"></a><a class="link" href="language.html#jam.language.rules.builtins.utility._precious__" title="PRECIOUS"><code class="literal">PRECIOUS</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule PRECIOUS ( <span class="emphasis"><em>targets</em></span> * )
</pre>
<p>
              The <code class="literal">PRECIOUS</code> rule specifies that each of the targets
              passed as the arguments should not be removed even if the command updating
              that target fails.
            </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.utility._pad__"></a><a class="link" href="language.html#jam.language.rules.builtins.utility._pad__" title="PAD"><code class="literal">PAD</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule PAD ( <span class="emphasis"><em>string</em></span> : <span class="emphasis"><em>width</em></span> )
</pre>
<p>
              If <span class="emphasis"><em>string</em></span> is shorter than <span class="emphasis"><em>width</em></span>
              characters, pads it with whitespace characters on the right, and returns
              the result. Otherwise, returns <span class="emphasis"><em>string</em></span> unmodified.
            </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.utility._file_open__"></a><a class="link" href="language.html#jam.language.rules.builtins.utility._file_open__" title="FILE_OPEN"><code class="literal">FILE_OPEN</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule FILE_OPEN ( <span class="emphasis"><em>filename</em></span> : <span class="emphasis"><em>mode</em></span> )
</pre>
<p>
              The <code class="literal">FILE_OPEN</code> rule opens the specified file and
              returns a file descriptor. The <span class="emphasis"><em>mode</em></span> parameter
              can be either "w" or "r". Note that at present,
              only the <code class="literal">UPDATE_NOW</code> rule can use the resulting file
              descriptor number.
            </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h6 class="title">
<a name="jam.language.rules.builtins.utility._update_now__"></a><a class="link" href="language.html#jam.language.rules.builtins.utility._update_now__" title="UPDATE_NOW"><code class="literal">UPDATE_NOW</code>
            </a>
</h6></div></div></div>
<pre class="programlisting">rule UPDATE_NOW ( <span class="emphasis"><em>targets</em></span> * : <span class="emphasis"><em>log</em></span> ? : <span class="emphasis"><em>ignore-minus-n</em></span> ? )
</pre>
<p>
              The <code class="literal">UPDATE_NOW</code> caused the specified targets to be
              updated immediately. If update was successfull, non-empty string is
              returned. The <span class="emphasis"><em>log</em></span> parameter, if present, specifies
              a descriptor of a file where all output from building is redirected.
              If the <span class="emphasis"><em>ignore-minus-n</em></span> parameter is specified,
              the targets are updated even if the <code class="literal">-n</code> parameter
              is specified on the command line.
            </p>
</div>
</div>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="jam.language.flow_of_control"></a><a class="link" href="language.html#jam.language.flow_of_control" title="Flow-of-Control">Flow-of-Control</a>
</h3></div></div></div>
<p>
        <code class="literal">BJam</code> has several simple flow-of-control statements:
      </p>
<pre class="programlisting">for <span class="emphasis"><em>var</em></span> in <span class="emphasis"><em>list</em></span> { <span class="emphasis"><em>statements</em></span> }
</pre>
<p>
        Executes <span class="emphasis"><em>statements</em></span> for each element in <span class="emphasis"><em>list</em></span>,
        setting the variable <span class="emphasis"><em>var</em></span> to the element value.
      </p>
<pre class="programlisting">if <span class="emphasis"><em>cond</em></span> { <span class="emphasis"><em>statements</em></span> }
[ else { <span class="emphasis"><em>statements</em></span> } ]
</pre>
<p>
        Does the obvious; the <code class="literal">else</code> clause is optional. <span class="emphasis"><em>cond</em></span>
        is built of:
      </p>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term"><code class="literal"><span class="emphasis"><em>a</em></span></code></span></dt>
<dd><p>
              true if any <span class="emphasis"><em>a</em></span> element is a non-zero-length string
            </p></dd>
<dt><span class="term"><code class="literal"><span class="emphasis"><em>a</em></span> = <span class="emphasis"><em>b</em></span></code></span></dt>
<dd><p>
              list <span class="emphasis"><em>a</em></span> matches list <span class="emphasis"><em>b</em></span> string-for-string
            </p></dd>
<dt><span class="term"><code class="literal"><span class="emphasis"><em>a</em></span> != <span class="emphasis"><em>b</em></span></code></span></dt>
<dd><p>
              list <span class="emphasis"><em>a</em></span> does not match list <span class="emphasis"><em>b</em></span>
            </p></dd>
<dt><span class="term"><code class="literal"><span class="emphasis"><em>a</em></span> &lt; <span class="emphasis"><em>b</em></span></code></span></dt>
<dd><p>
              <span class="emphasis"><em>a[i]</em></span> string is less than <span class="emphasis"><em>b[i]</em></span>
              string, where <span class="emphasis"><em>i</em></span> is first mismatched element in
              lists <span class="emphasis"><em>a</em></span> and <span class="emphasis"><em>b</em></span>
            </p></dd>
<dt><span class="term"><code class="literal"><span class="emphasis"><em>a</em></span> &lt;= <span class="emphasis"><em>b</em></span></code></span></dt>
<dd><p>
              every <span class="emphasis"><em>a</em></span> string is less than or equal to its <span class="emphasis"><em>b</em></span>
              counterpart
            </p></dd>
<dt><span class="term"><code class="literal"><span class="emphasis"><em>a</em></span> &gt; <span class="emphasis"><em>b</em></span></code></span></dt>
<dd><p>
              <span class="emphasis"><em>a[i]</em></span> string is greater than <span class="emphasis"><em>b[i]</em></span>
              string, where <span class="emphasis"><em>i</em></span> is first mismatched element
            </p></dd>
<dt><span class="term"><code class="literal"><span class="emphasis"><em>a</em></span> &gt;= <span class="emphasis"><em>b</em></span></code></span></dt>
<dd><p>
              every <span class="emphasis"><em>a</em></span> string is greater than or equal to its
              <span class="emphasis"><em>b</em></span> counterpart
            </p></dd>
<dt><span class="term"><code class="literal"><span class="emphasis"><em>a</em></span> in <span class="emphasis"><em>b</em></span></code></span></dt>
<dd><p>
              true if all elements of <span class="emphasis"><em>a</em></span> can be found in <span class="emphasis"><em>b</em></span>,
              or if <span class="emphasis"><em>a</em></span> has no elements
            </p></dd>
<dt><span class="term"><code class="literal">! <span class="emphasis"><em>cond</em></span></code></span></dt>
<dd><p>
              condition not true
            </p></dd>
<dt><span class="term"><code class="literal"><span class="emphasis"><em>cond</em></span> &amp;&amp; <span class="emphasis"><em>cond</em></span></code></span></dt>
<dd><p>
              conjunction
            </p></dd>
<dt><span class="term"><code class="literal"><span class="emphasis"><em>cond</em></span> || <span class="emphasis"><em>cond</em></span></code></span></dt>
<dd><p>
              disjunction
            </p></dd>
<dt><span class="term"><code class="literal">( <span class="emphasis"><em>cond</em></span> )</code></span></dt>
<dd><p>
              precedence grouping
            </p></dd>
</dl>
</div>
<pre class="programlisting">include <span class="emphasis"><em>file</em></span> ;
</pre>
<p>
        Causes <code class="literal">bjam</code> to read the named <span class="emphasis"><em>file</em></span>.
        The <span class="emphasis"><em>file</em></span> is bound like a regular target (see Binding
        above) but unlike a regular target the include <span class="emphasis"><em>file</em></span>
        cannot be built.
      </p>
<p>
        The include <span class="emphasis"><em>file</em></span> is inserted into the input stream during
        the parsing phase. The primary input file and all the included file(s) are
        treated as a single file; that is, jam infers no scope boundaries from included
        files.
      </p>
<pre class="programlisting">local <span class="emphasis"><em>vars</em></span> [ = <span class="emphasis"><em>values</em></span> ] ;
</pre>
<p>
        Creates new <span class="emphasis"><em>vars</em></span> inside to the enclosing <code class="literal">{}</code>
        block, obscuring any previous values they might have. The previous values
        for vars are restored when the current block ends. Any rule called or file
        included will see the local and not the previous value (this is sometimes
        called Dynamic Scoping). The local statement may appear anywhere, even outside
        of a block (in which case the previous value is restored when the input ends).
        The <span class="emphasis"><em>vars</em></span> are initialized to <span class="emphasis"><em>values</em></span>
        if present, or left uninitialized otherwise.
      </p>
<pre class="programlisting">return <span class="emphasis"><em>values</em></span> ;
</pre>
<p>
        Within a rule body, the return statement sets the return value for an invocation
        of the rule. It does <span class="bold"><strong>not</strong></span> cause the rule
        to return; a rule's value is actually the value of the last statement executed,
        so a return should be the last statement executed before the rule "naturally"
        returns.
      </p>
<pre class="programlisting">switch <span class="emphasis"><em>value</em></span>
{
    case <span class="emphasis"><em>pattern1</em></span> : <span class="emphasis"><em>statements</em></span> ;
    case <span class="emphasis"><em>pattern2</em></span> : <span class="emphasis"><em>statements</em></span> ;
    ...
}
</pre>
<p>
        The switch statement executes zero or one of the enclosed <span class="emphasis"><em>statements</em></span>,
        depending on which, if any, is the first case whose <span class="emphasis"><em>pattern</em></span>
        matches <span class="emphasis"><em>value</em></span>. The <span class="emphasis"><em>pattern</em></span> values
        are not variable-expanded. The pattern values may include the following wildcards:
      </p>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term"><code class="literal">?</code></span></dt>
<dd><p>
              match any single character
            </p></dd>
<dt><span class="term"><code class="literal">*</code></span></dt>
<dd><p>
              match zero or more characters
            </p></dd>
<dt><span class="term"><code class="literal">[<span class="emphasis"><em>chars</em></span>]</code></span></dt>
<dd><p>
              match any single character in <span class="emphasis"><em>chars</em></span>
            </p></dd>
<dt><span class="term"><code class="literal">[^<span class="emphasis"><em>chars</em></span>]</code></span></dt>
<dd><p>
              match any single character not in <span class="emphasis"><em>chars</em></span>
            </p></dd>
<dt><span class="term"><code class="literal">\<span class="emphasis"><em>x</em></span></code></span></dt>
<dd><p>
              match <span class="emphasis"><em>x</em></span> (escapes the other wildcards)
            </p></dd>
</dl>
</div>
<pre class="programlisting">while <span class="emphasis"><em>cond</em></span> { <span class="emphasis"><em>statements</em></span> }
</pre>
<p>
        Repeatedly execute <span class="emphasis"><em>statements</em></span> while <span class="emphasis"><em>cond</em></span>
        remains true upon entry. (See the description of <span class="emphasis"><em>cond</em></span>
        expression syntax under if, above).
      </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="jam.language.variables"></a><a class="link" href="language.html#jam.language.variables" title="Variables">Variables</a>
</h3></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="language.html#jam.language.variables.expansion">Variable Expansion</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.variables.local_for_loop_variables">Local
        For Loop Variables</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.variables.atfile">Generated File Expansion</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.variables.builtins">Built-in Variables</a></span></dt>
</dl></div>
<p>
        <code class="literal">BJam</code> variables are lists of zero or more elements, with
        each element being a string value. An undefined variable is indistinguishable
        from a variable with an empty list, however, a defined variable may have
        one more elements which are null strings. All variables are referenced as
        <code class="literal">$(<span class="emphasis"><em>variable</em></span>)</code>.
      </p>
<p>
        Variables are either global or target-specific. In the latter case, the variable
        takes on the given value only during the updating of the specific target.
      </p>
<p>
        A variable is defined with:
      </p>
<pre class="programlisting"><span class="emphasis"><em>variable</em></span> = <span class="emphasis"><em>elements</em></span> ;
<span class="emphasis"><em>variable</em></span> += <span class="emphasis"><em>elements</em></span> ;
<span class="emphasis"><em>variable</em></span> on <span class="emphasis"><em>targets</em></span> = <span class="emphasis"><em>elements</em></span> ;
<span class="emphasis"><em>variable</em></span> on <span class="emphasis"><em>targets</em></span> += <span class="emphasis"><em>elements</em></span> ;
<span class="emphasis"><em>variable</em></span> default = <span class="emphasis"><em>elements</em></span> ;
<span class="emphasis"><em>variable</em></span> ?= <span class="emphasis"><em>elements</em></span> ;
</pre>
<p>
        The first two forms set <span class="emphasis"><em>variable</em></span> globally. The third
        and forth forms set a target-specific variable. The <code class="literal">=</code>
        operator replaces any previous elements of <span class="emphasis"><em>variable</em></span>
        with <span class="emphasis"><em>elements</em></span>; the <code class="literal">+=</code> operation adds
        <span class="emphasis"><em>elements</em></span> to <span class="emphasis"><em>variable</em></span>'s list of
        elements. The final two forms are synonymous: they set <span class="emphasis"><em>variable</em></span>
        globally, but only if it was previously unset.
      </p>
<p>
        Variables referenced in updating commands will be replaced with their values;
        target-specific values take precedence over global values. Variables passed
        as arguments (<code class="literal">$(1)</code> and <code class="literal">$(2)</code>) to actions
        are replaced with their bound values; the "<code class="literal">bind</code>"
        modifier can be used on actions to cause other variables to be replaced with
        bound values. See Action Modifiers above.
      </p>
<p>
        <code class="literal">BJam</code> variables are not re-exported to the environment
        of the shell that executes the updating actions, but the updating actions
        can reference <code class="literal">bjam</code> variables with <code class="literal">$(<span class="emphasis"><em>variable</em></span>)</code>.
      </p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="jam.language.variables.expansion"></a><a class="link" href="language.html#jam.language.variables.expansion" title="Variable Expansion">Variable Expansion</a>
</h4></div></div></div>
<p>
          During parsing, <code class="literal">bjam</code> performs variable expansion on
          each token that is not a keyword or rule name. Such tokens with embedded
          variable references are replaced with zero or more tokens. Variable references
          are of the form <code class="literal">$(<span class="emphasis"><em>v</em></span>)</code> or <code class="literal">$(<span class="emphasis"><em>vm</em></span>)</code>,
          where <span class="emphasis"><em>v</em></span> is the variable name, and <span class="emphasis"><em>m</em></span>
          are optional modifiers.
        </p>
<p>
          Variable expansion in a rule's actions is similar to variable expansion
          in statements, except that the action string is tokenized at whitespace
          regardless of quoting.
        </p>
<p>
          The result of a token after variable expansion is the <span class="emphasis"><em>product</em></span>
          of the components of the token, where each component is a literal substring
          or a list substituting a variable reference. For example:
        </p>
<pre class="programlisting">$(X) -&gt; a b c
t$(X) -&gt; ta tb tc
$(X)z -&gt; az bz cz
$(X)-$(X) -&gt; a-a a-b a-c b-a b-b b-c c-a c-b c-c
</pre>
<p>
          The variable name and modifiers can themselves contain a variable reference,
          and this partakes of the product as well:
        </p>
<pre class="programlisting">$(X) -&gt; a b c
$(Y) -&gt; 1 2
$(Z) -&gt; X Y
$($(Z)) -&gt; a b c 1 2
</pre>
<p>
          Because of this product expansion, if any variable reference in a token
          is undefined, the result of the expansion is an empty list. If any variable
          element is a null string, the result propagates the non-null elements:
        </p>
<pre class="programlisting">$(X) -&gt; a ""
$(Y) -&gt; "" 1
$(Z) -&gt;
-$(X)$(Y)- -&gt; -a- -a1- -- -1-
-$(X)$(Z)- -&gt;
</pre>
<p>
          A variable element's string value can be parsed into grist and filename-related
          components. Modifiers to a variable are used to select elements, select
          components, and replace components. The modifiers are:
        </p>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term"><code class="literal">[<span class="emphasis"><em>n</em></span>]</code></span></dt>
<dd><p>
                Select element number <span class="emphasis"><em>n</em></span> (starting at 1). If
                the variable contains fewer than <span class="emphasis"><em>n</em></span> elements,
                the result is a zero-element list. <span class="emphasis"><em>n</em></span> can be
                negative in which case the element number <span class="emphasis"><em>n</em></span>
                from the last leftward is returned.
              </p></dd>
<dt><span class="term"><code class="literal">[<span class="emphasis"><em>n</em></span>-<span class="emphasis"><em>m</em></span>]</code></span></dt>
<dd><p>
                Select elements number <span class="emphasis"><em>n</em></span> through <span class="emphasis"><em>m</em></span>.
                <span class="emphasis"><em>n</em></span> and <span class="emphasis"><em>m</em></span> can be negative
                in which case they refer to elements counting from the last leftward.
              </p></dd>
<dt><span class="term"><code class="literal">[<span class="emphasis"><em>n</em></span>-]</code></span></dt>
<dd><p>
                Select elements number <span class="emphasis"><em>n</em></span> through the last.
                <span class="emphasis"><em>n</em></span> can be negative in which case it refers to
                the element counting from the last leftward.
              </p></dd>
<dt><span class="term"><code class="literal">:B</code></span></dt>
<dd><p>
                Select filename base.
              </p></dd>
<dt><span class="term"><code class="literal">:S</code></span></dt>
<dd><p>
                Select (last) filename suffix.
              </p></dd>
<dt><span class="term"><code class="literal">:M</code></span></dt>
<dd><p>
                Select archive member name.
              </p></dd>
<dt><span class="term"><code class="literal">:D</code></span></dt>
<dd><p>
                Select directory path.
              </p></dd>
<dt><span class="term"><code class="literal">:P</code></span></dt>
<dd><p>
                Select parent directory.
              </p></dd>
<dt><span class="term"><code class="literal">:G</code></span></dt>
<dd><p>
                Select grist.
              </p></dd>
<dt><span class="term"><code class="literal">:U</code></span></dt>
<dd><p>
                Replace lowercase characters with uppercase.
              </p></dd>
<dt><span class="term"><code class="literal">:L</code></span></dt>
<dd><p>
                Replace uppercase characters with lowercase.
              </p></dd>
<dt><span class="term"><code class="literal">:T</code></span></dt>
<dd>
<p>
                Converts all back-slashes ("\") to forward slashes ("/").
                For example
</p>
<pre class="programlisting"><span class="identifier">x</span> <span class="special">=</span> <span class="string">"C:\\Program Files\\Borland"</span> <span class="special">;</span> <span class="identifier">ECHO</span> <span class="error">$</span><span class="special">(</span><span class="identifier">x</span><span class="special">:</span><span class="identifier">T</span><span class="special">)</span> <span class="special">;</span>
</pre>
<p>
                prints <code class="literal">"C:/Program Files/Borland"</code>
              </p>
</dd>
<dt><span class="term"><code class="literal">:W</code></span></dt>
<dd>
<p>
                When invoking Windows-based tools from <a href="http://www.cygwin.com/" target="_top">Cygwin</a>
                it can be important to pass them true windows-style paths. The <code class="literal">:W</code>
                modifier, <span class="bold"><strong>under Cygwin only</strong></span>, turns
                a cygwin path into a Win32 path using the <a href="http://www.cygwin.com/cygwin-api/func-cygwin-conv-to-win32-path.html" target="_top"><code class="literal">cygwin_conv_to_win32_path</code></a>
                function. On other platforms, the string is unchanged. For example
</p>
<pre class="programlisting"><span class="identifier">x</span> <span class="special">=</span> <span class="string">"/cygdrive/c/Program Files/Borland"</span> <span class="special">;</span> <span class="identifier">ECHO</span> <span class="error">$</span><span class="special">(</span><span class="identifier">x</span><span class="special">:</span><span class="identifier">W</span><span class="special">)</span> <span class="special">;</span>
</pre>
<p>
                prints <code class="literal">"C:\Program Files\Borland"</code> on
                Cygwin
              </p>
</dd>
<dt><span class="term"><code class="literal">:<span class="emphasis"><em>chars</em></span></code></span></dt>
<dd><p>
                Select the components listed in <span class="emphasis"><em>chars</em></span>.
              </p></dd>
<dt><span class="term"><code class="literal">:G=<span class="emphasis"><em>grist</em></span></code></span></dt>
<dd><p>
                Replace grist with <span class="emphasis"><em>grist</em></span>.
              </p></dd>
<dt><span class="term"><code class="literal">:D=<span class="emphasis"><em>path</em></span></code></span></dt>
<dd><p>
                Replace directory with <span class="emphasis"><em>path</em></span>.
              </p></dd>
<dt><span class="term"><code class="literal">:B=<span class="emphasis"><em>base</em></span></code></span></dt>
<dd><p>
                Replace the base part of file name with <span class="emphasis"><em>base</em></span>.
              </p></dd>
<dt><span class="term"><code class="literal">:S=<span class="emphasis"><em>suf</em></span></code></span></dt>
<dd><p>
                Replace the suffix of file name with <span class="emphasis"><em>suf</em></span>.
              </p></dd>
<dt><span class="term"><code class="literal">:M=<span class="emphasis"><em>mem</em></span></code></span></dt>
<dd><p>
                Replace the archive member name with <span class="emphasis"><em>mem</em></span>.
              </p></dd>
<dt><span class="term"><code class="literal">:R=<span class="emphasis"><em>root</em></span></code></span></dt>
<dd><p>
                Prepend <span class="emphasis"><em>root</em></span> to the whole file name, if not
                already rooted.
              </p></dd>
<dt><span class="term"><code class="literal">:E=<span class="emphasis"><em>value</em></span></code></span></dt>
<dd><p>
                Assign <span class="emphasis"><em>value</em></span> to the variable if it is unset.
              </p></dd>
<dt><span class="term"><code class="literal">:J=<span class="emphasis"><em>joinval</em></span></code></span></dt>
<dd><p>
                Concatentate list elements into single element, separated by <span class="emphasis"><em>joinval</em></span>'.
              </p></dd>
</dl>
</div>
<p>
          On VMS, <code class="literal">$(var:P)</code> is the parent directory of <code class="literal">$(var:D)</code>.
        </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="jam.language.variables.local_for_loop_variables"></a><a class="link" href="language.html#jam.language.variables.local_for_loop_variables" title="Local For Loop Variables">Local
        For Loop Variables</a>
</h4></div></div></div>
<p>
          Boost Jam allows you to declare a local for loop control variable right
          in the loop:
        </p>
<pre class="programlisting">x = 1 2 3 ;
y = 4 5 6 ;
for <span class="bold"><strong>local</strong></span> y in $(x)
{
    ECHO $(y) ; # prints "1", "2", or "3"
}
ECHO $(y) ;     # prints "4 5 6"
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="jam.language.variables.atfile"></a><a class="link" href="language.html#jam.language.variables.atfile" title="Generated File Expansion">Generated File Expansion</a>
</h4></div></div></div>
<p>
          During expansion of expressions <code class="literal">bjam</code> also looks for
          subexpressions of the form <code class="literal">@(filename:E=filecontents)</code>
          and replaces the expression with <code class="literal">filename</code> after creating
          the given file with the contents set to <code class="literal">filecontents</code>.
          This is useful for creating compiler response files, and other "internal"
          files. The expansion works both during parsing and action execution. Hence
          it is possible to create files during any of the three build phases.
        </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="jam.language.variables.builtins"></a><a class="link" href="language.html#jam.language.variables.builtins" title="Built-in Variables">Built-in Variables</a>
</h4></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="language.html#jam.language.variables.builtins.search">SEARCH and
          LOCATE</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.variables.builtins.hdrscan">HDRSCAN
          and HDRRULE</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.variables.builtins.semaphores">Semaphores</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.variables.builtins.platform_identifier">Platform
          Identifier</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.variables.builtins.jam_version">Jam
          Version</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.variables.builtins.jamshell">JAMSHELL</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.variables.builtins.actionrule"><code class="literal">__TIMING_RULE__</code>
          and <code class="literal">__ACTION_RULE__</code></a></span></dt>
</dl></div>
<p>
          This section discusses variables that have special meaning to <code class="literal">bjam</code>.
          All of these must be defined or used in the global module -- using those
          variables inside a named module will not have the desired effect. See
          <a class="link" href="language.html#jam.language.modules" title="Modules">Modules</a>.
        </p>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="jam.language.variables.builtins.search"></a><a class="link" href="language.html#jam.language.variables.builtins.search" title="SEARCH and LOCATE">SEARCH and
          LOCATE</a>
</h5></div></div></div>
<p>
            These two variables control the binding of file target names to locations
            in the file system. Generally, <code class="literal">$(SEARCH)</code> is used to
            find existing sources while <code class="literal">$(LOCATE)</code> is used to fix
            the location for built targets.
          </p>
<p>
            Rooted (absolute path) file targets are bound as is. Unrooted file target
            names are also normally bound as is, and thus relative to the current
            directory, but the settings of <code class="literal">$(LOCATE)</code> and <code class="literal">$(SEARCH)</code>
            alter this:
          </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
                If <code class="literal">$(LOCATE)</code> is set then the target is bound relative
                to the first directory in <code class="literal">$(LOCATE)</code>. Only the
                first element is used for binding.
              </li>
<li class="listitem">
                If <code class="literal">$(SEARCH)</code> is set then the target is bound to
                the first directory in <code class="literal">$(SEARCH)</code> where the target
                file already exists.
              </li>
<li class="listitem">
                If the <code class="literal">$(SEARCH)</code> search fails, the target is bound
                relative to the current directory anyhow.
              </li>
</ul></div>
<p>
            Both <code class="literal">$(SEARCH)</code> and <code class="literal">$(LOCATE)</code> should
            be set target-specific and not globally. If they were set globally,
            <code class="literal">bjam</code> would use the same paths for all file binding,
            which is not likely to produce sane results. When writing your own rules,
            especially ones not built upon those in Jambase, you may need to set
            <code class="literal">$(SEARCH)</code> or <code class="literal">$(LOCATE)</code> directly.
            Almost all of the rules defined in Jambase set <code class="literal">$(SEARCH)</code>
            and <code class="literal">$(LOCATE)</code> to sensible values for sources they
            are looking for and targets they create, respectively.
          </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="jam.language.variables.builtins.hdrscan"></a><a class="link" href="language.html#jam.language.variables.builtins.hdrscan" title="HDRSCAN and HDRRULE">HDRSCAN
          and HDRRULE</a>
</h5></div></div></div>
<p>
            These two variables control header file scanning. <code class="literal">$(HDRSCAN)</code>
            is an <code class="literal">egrep(1)</code> pattern, with ()'s surrounding the
            file name, used to find file inclusion statements in source files. <code class="literal">Jambase</code>
            uses <code class="literal">$(HDRPATTERN)</code> as the pattern for <code class="literal">$(HDRSCAN)</code>.
            <code class="literal">$(HDRRULE)</code> is the name of a rule to invoke with the
            results of the scan: the scanned file is the target, the found files
            are the sources. This is the only place where <code class="literal">bjam</code>
            invokes a rule through a variable setting.
          </p>
<p>
            Both <code class="literal">$(HDRSCAN)</code> and <code class="literal">$(HDRRULE)</code>
            must be set for header file scanning to take place, and they should be
            set target-specific and not globally. If they were set globally, all
            files, including executables and libraries, would be scanned for header
            file include statements.
          </p>
<p>
            The scanning for header file inclusions is not exact, but it is at least
            dynamic, so there is no need to run something like <code class="literal">makedepend(GNU)</code>
            to create a static dependency file. The scanning mechanism errs on the
            side of inclusion (i.e., it is more likely to return filenames that are
            not actually used by the compiler than to miss include files) because
            it can't tell if <code class="computeroutput"><span class="preprocessor">#include</span></code>
            lines are inside <code class="computeroutput"><span class="preprocessor">#ifdefs</span></code>
            or other conditional logic. In <code class="literal">Jambase</code>, <code class="literal">HdrRule</code>
            applies the <code class="literal">NOCARE</code> rule to each header file found
            during scanning so that if the file isn't present yet doesn't cause the
            compilation to fail, <code class="literal">bjam</code> won't care.
          </p>
<p>
            Also, scanning for regular expressions only works where the included
            file name is literally in the source file. It can't handle languages
            that allow including files using variable names (as the <code class="literal">Jam</code>
            language itself does).
          </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="jam.language.variables.builtins.semaphores"></a><a class="link" href="language.html#jam.language.variables.builtins.semaphores" title="Semaphores">Semaphores</a>
</h5></div></div></div>
<p>
            It is sometimes desirable to disallow parallel execution of some actions.
            For example:
          </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
                Old versions of yacc use files with fixed names. So, running two
                yacc actions is dangerous.
              </li>
<li class="listitem">
                One might want to perform parallel compiling, but not do parallel
                linking, because linking is i/o bound and only gets slower.
              </li>
</ul></div>
<p>
            Craig McPeeters has extended Perforce Jam to solve such problems, and
            that extension was integrated in Boost.Jam.
          </p>
<p>
            Any target can be assigned a <span class="emphasis"><em>semaphore</em></span>, by setting
            a variable called <code class="literal">SEMAPHORE</code> on that target. The value
            of the variable is the semaphore name. It must be different from names
            of any declared target, but is arbitrary otherwise.
          </p>
<p>
            The semantic of semaphores is that in a group of targets which have the
            same semaphore, only one can be updated at the moment, regardless of
            "<code class="literal">-j</code>" option.
          </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="jam.language.variables.builtins.platform_identifier"></a><a class="link" href="language.html#jam.language.variables.builtins.platform_identifier" title="Platform Identifier">Platform
          Identifier</a>
</h5></div></div></div>
<p>
            A number of Jam built-in variables can be used to identify runtime platform:
          </p>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term"><code class="literal">OS</code></span></dt>
<dd><p>
                  OS identifier string
                </p></dd>
<dt><span class="term"><code class="literal">OSPLAT</code></span></dt>
<dd><p>
                  Underlying architecture, when applicable
                </p></dd>
<dt><span class="term"><code class="literal">MAC</code></span></dt>
<dd><p>
                  true on MAC platform
                </p></dd>
<dt><span class="term"><code class="literal">NT</code></span></dt>
<dd><p>
                  true on NT platform
                </p></dd>
<dt><span class="term"><code class="literal">OS2</code></span></dt>
<dd><p>
                  true on OS2 platform
                </p></dd>
<dt><span class="term"><code class="literal">UNIX</code></span></dt>
<dd><p>
                  true on Unix platforms
                </p></dd>
<dt><span class="term"><code class="literal">VMS</code></span></dt>
<dd><p>
                  true on VMS platform
                </p></dd>
</dl>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="jam.language.variables.builtins.jam_version"></a><a class="link" href="language.html#jam.language.variables.builtins.jam_version" title="Jam Version">Jam
          Version</a>
</h5></div></div></div>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term"><code class="literal">JAMDATE</code></span></dt>
<dd><p>
                  Time and date at <code class="literal">bjam</code> start-up as an ISO-8601
                  UTC value.
                </p></dd>
<dt><span class="term"><code class="literal">JAMUNAME</code></span></dt>
<dd><p>
                  Ouput of uname(1) command (Unix only)
                </p></dd>
<dt><span class="term"><code class="literal">JAMVERSION</code></span></dt>
<dd><p>
                  <code class="literal">bjam</code> version, currently "3.1.19"
                </p></dd>
<dt><span class="term"><code class="literal">JAM_VERSION</code></span></dt>
<dd><p>
                  A predefined global variable with two elements indicates the version
                  number of Boost Jam. Boost Jam versions start at "<code class="literal">03</code>"
                  "<code class="literal">00</code>". Earlier versions of <code class="literal">Jam</code>
                  do not automatically define <code class="literal">JAM_VERSION</code>.
                </p></dd>
</dl>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="jam.language.variables.builtins.jamshell"></a><a class="link" href="language.html#jam.language.variables.builtins.jamshell" title="JAMSHELL">JAMSHELL</a>
</h5></div></div></div>
<p>
            When <code class="literal">bjam</code> executes a rule's action block, it forks
            and execs a shell, passing the action block as an argument to the shell.
            The invocation of the shell can be controlled by <code class="literal">$(JAMSHELL)</code>.
            The default on Unix is, for example:
          </p>
<pre class="programlisting">JAMSHELL = /bin/sh -c % ;
</pre>
<p>
            The <code class="literal">%</code> is replaced with the text of the action block.
          </p>
<p>
            <code class="literal">BJam</code> does not directly support building in parallel
            across multiple hosts, since that is heavily dependent on the local environment.
            To build in parallel across multiple hosts, you need to write your own
            shell that provides access to the multiple hosts. You then reset <code class="literal">$(JAMSHELL)</code>
            to reference it.
          </p>
<p>
            Just as <code class="literal">bjam</code> expands a <code class="literal">%</code> to be
            the text of the rule's action block, it expands a <code class="literal">!</code>
            to be the multi-process slot number. The slot number varies between 1
            and the number of concurrent jobs permitted by the <code class="literal">-j</code>
            flag given on the command line. Armed with this, it is possible to write
            a multiple host shell. For example:
          </p>
<pre class="programlisting">#!/bin/sh

# This sample JAMSHELL uses the SunOS on(1) command to execute a
# command string with an identical environment on another host.

# Set JAMSHELL = jamshell ! %
#
# where jamshell is the name of this shell file.
#
# This version handles up to -j6; after that they get executed
# locally.

case $1 in
1|4) on winken sh -c "$2";;
2|5) on blinken sh -c "$2";;
3|6) on nod sh -c "$2";;
*) eval "$2";;
esac
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="jam.language.variables.builtins.actionrule"></a><a class="link" href="language.html#jam.language.variables.builtins.actionrule" title="__TIMING_RULE__ and __ACTION_RULE__"><code class="literal">__TIMING_RULE__</code>
          and <code class="literal">__ACTION_RULE__</code></a>
</h5></div></div></div>
<p>
            The <code class="literal">__TIMING_RULE__</code> and <code class="literal">__ACTION_RULE__</code>
            can be set to the name of a rule for <code class="literal">bjam</code> to call
            <span class="bold"><strong>after</strong></span> an action completes for a target.
            They both give diagnostic information about the action that completed.
            For <code class="literal">__TIMING_RULE__</code> the rule is called as:
          </p>
<pre class="programlisting"><span class="identifier">rule</span> <span class="identifier">timing</span><span class="special">-</span><span class="identifier">rule</span> <span class="special">(</span> <span class="identifier">args</span> <span class="special">*</span> <span class="special">:</span> <span class="identifier">target</span> <span class="special">:</span> <span class="identifier">start</span> <span class="identifier">end</span> <span class="identifier">user</span> <span class="identifier">system</span> <span class="special">)</span>
</pre>
<p>
            And <code class="literal">__ACTION_RULE__</code> is called as:
          </p>
<pre class="programlisting"><span class="identifier">rule</span> <span class="identifier">action</span><span class="special">-</span><span class="identifier">rule</span> <span class="special">(</span> <span class="identifier">args</span> <span class="special">*</span> <span class="special">:</span> <span class="identifier">target</span> <span class="special">:</span> <span class="identifier">command</span> <span class="identifier">status</span> <span class="identifier">start</span> <span class="identifier">end</span> <span class="identifier">user</span> <span class="identifier">system</span> <span class="special">:</span> <span class="identifier">output</span> <span class="special">?</span> <span class="special">)</span>
</pre>
<p>
            The arguments for both are:
          </p>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term"><code class="literal">args</code></span></dt>
<dd><p>
                  Any values following the rule name in the <code class="literal">__TIMING_RULE__</code>
                  or <code class="literal">__ACTION_RULE__</code> are passed along here.
                </p></dd>
<dt><span class="term"><code class="literal">target</code></span></dt>
<dd><p>
                  The <code class="literal">bjam</code> target that was built.
                </p></dd>
<dt><span class="term"><code class="literal">command</code></span></dt>
<dd><p>
                  The text of the executed command in the action body.
                </p></dd>
<dt><span class="term"><code class="literal">status</code></span></dt>
<dd><p>
                  The integer result of the executed command.
                </p></dd>
<dt><span class="term"><code class="literal">start</code></span></dt>
<dd><p>
                  The starting timestamp of the executed command as a ISO-8601 UTC
                  value.
                </p></dd>
<dt><span class="term"><code class="literal">end</code></span></dt>
<dd><p>
                  The completion timestamp of the executed command as a ISO-8601
                  UTC value.
                </p></dd>
<dt><span class="term"><code class="literal">user</code></span></dt>
<dd><p>
                  The number of user CPU seconds the executed command spent as a
                  floating point value.
                </p></dd>
<dt><span class="term"><code class="literal">system</code></span></dt>
<dd><p>
                  The number of system CPU seconds the executed command spent as
                  a floating point value.
                </p></dd>
<dt><span class="term"><code class="literal">output</code></span></dt>
<dd><p>
                  The output of the command as a single string. The content of the
                  output reflects the use of the <code class="literal">-pX</code> option.
                </p></dd>
</dl>
</div>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
              If both variables are set for a target both are called, first <code class="literal">__TIMING_RULE__</code>
              then <code class="literal">__ACTION_RULE__</code>.
            </p></td></tr>
</table></div>
</div>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="jam.language.modules"></a><a class="link" href="language.html#jam.language.modules" title="Modules">Modules</a>
</h3></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="language.html#jam.language.modules.declaration">Declaration</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.modules.variable_scope">Variable Scope</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.modules.local_rules">Local Rules</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.modules.the__rulenames__rule">The <code class="literal">RULENAMES</code>
        Rule</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.modules.the__varnames__rule">The <code class="literal">VARNAMES</code>
        Rule</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.modules.the__import__rule">The <code class="literal">IMPORT</code>
        Rule</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.modules.the__export__rule">The <code class="literal">EXPORT</code>
        Rule</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.modules.the__caller_module__rule">The
        <code class="literal">CALLER_MODULE</code> Rule</a></span></dt>
<dt><span class="section"><a href="language.html#jam.language.modules.the__delete_module__rule">The
        <code class="literal">DELETE_MODULE</code> Rule</a></span></dt>
</dl></div>
<p>
        Boost Jam introduces support for modules, which provide some rudimentary
        namespace protection for rules and variables. A new keyword, "<code class="literal">module</code>"
        was also introduced. The features described in this section are primitives,
        meaning that they are meant to provide the operations needed to write Jam
        rules which provide a more elegant module interface.
      </p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="jam.language.modules.declaration"></a><a class="link" href="language.html#jam.language.modules.declaration" title="Declaration">Declaration</a>
</h4></div></div></div>
<pre class="programlisting">module <span class="emphasis"><em>expression</em></span> { ... }
</pre>
<p>
          Code within the <code class="literal">{ ... }</code> executes within the module named
          by evaluating expression. Rule definitions can be found in the module's
          own namespace, and in the namespace of the global module as <span class="emphasis"><em>module-name</em></span>.<span class="emphasis"><em>rule-name</em></span>,
          so within a module, other rules in that module may always be invoked without
          qualification:
        </p>
<pre class="programlisting"><span class="bold"><strong>module my_module</strong></span>
<span class="bold"><strong>{</strong></span>
    rule salute ( x ) { ECHO $(x), world ; }
    rule greet ( ) { salute hello ; }
    greet ;
<span class="bold"><strong>}</strong></span>
<span class="bold"><strong>my_module.salute</strong></span> goodbye ;
</pre>
<p>
          When an invoked rule is not found in the current module's namespace, it
          is looked up in the namespace of the global module, so qualified calls
          work across modules:
        </p>
<pre class="programlisting">module your_module
{
    rule bedtime ( ) { <span class="bold"><strong>my_module.salute</strong></span> goodnight ; }
}
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="jam.language.modules.variable_scope"></a><a class="link" href="language.html#jam.language.modules.variable_scope" title="Variable Scope">Variable Scope</a>
</h4></div></div></div>
<p>
          Each module has its own set of dynamically nested variable scopes. When
          execution passes from module A to module B, all the variable bindings from
          A become unavailable, and are replaced by the bindings that belong to B.
          This applies equally to local and global variables:
        </p>
<pre class="programlisting">module A
{
    x = 1 ;
    rule f ( )
    {
        local y = 999 ; # becomes visible again when B.f calls A.g
        B.f ;
    }
    rule g ( )
    {
        ECHO $(y) ;     # prints "999"
    }
}
module B
{
    y = 2 ;
    rule f ( )
    {
        ECHO $(y) ; # always prints "2"
        A.g ;
    }
}
</pre>
<p>
          The only way to access another module's variables is by entering that module:
        </p>
<pre class="programlisting">rule peek ( module-name ? : variables + )
{
    module $(module-name)
    {
        return $($(&gt;)) ;
    }
}
</pre>
<p>
          Note that because existing variable bindings change whenever a new module
          scope is entered, argument bindings become unavailable. That explains the
          use of "<code class="literal">$(&gt;)</code>" in the peek rule above.
        </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="jam.language.modules.local_rules"></a><a class="link" href="language.html#jam.language.modules.local_rules" title="Local Rules">Local Rules</a>
</h4></div></div></div>
<pre class="programlisting">local rule <span class="emphasis"><em>rulename</em></span>...
</pre>
<p>
          The rule is declared locally to the current module. It is not entered in
          the global module with qualification, and its name will not appear in the
          result of:
        </p>
<pre class="programlisting">[ RULENAMES <span class="emphasis"><em>module-name</em></span> ]
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="jam.language.modules.the__rulenames__rule"></a><a class="link" href="language.html#jam.language.modules.the__rulenames__rule" title="The RULENAMES Rule">The <code class="literal">RULENAMES</code>
        Rule</a>
</h4></div></div></div>
<pre class="programlisting">rule RULENAMES ( <span class="emphasis"><em>module</em></span> ? )
</pre>
<p>
          Returns a list of the names of all non-local rules in the given module.
          If <span class="emphasis"><em>module</em></span> is omitted, the names of all non-local rules
          in the global module are returned.
        </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="jam.language.modules.the__varnames__rule"></a><a class="link" href="language.html#jam.language.modules.the__varnames__rule" title="The VARNAMES Rule">The <code class="literal">VARNAMES</code>
        Rule</a>
</h4></div></div></div>
<pre class="programlisting">rule VARNAMES ( <span class="emphasis"><em>module</em></span> ? )
</pre>
<p>
          Returns a list of the names of all variable bindings in the given module.
          If <span class="emphasis"><em>module</em></span> is omitted, the names of all variable bindings
          in the global module are returned.
        </p>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
            This includes any local variables in rules from the call stack which
            have not returned at the time of the <code class="literal">VARNAMES</code> invocation.
          </p></td></tr>
</table></div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="jam.language.modules.the__import__rule"></a><a class="link" href="language.html#jam.language.modules.the__import__rule" title="The IMPORT Rule">The <code class="literal">IMPORT</code>
        Rule</a>
</h4></div></div></div>
<p>
          <code class="literal">IMPORT</code> allows rule name aliasing across modules:
        </p>
<pre class="programlisting">rule IMPORT ( <span class="emphasis"><em>source_module</em></span> ? : <span class="emphasis"><em>source_rules</em></span> *
            : <span class="emphasis"><em>target_module</em></span> ? : <span class="emphasis"><em>target_rules</em></span> * )
</pre>
<p>
          The <code class="literal">IMPORT</code> rule copies rules from the <span class="emphasis"><em>source_module</em></span>
          into the <span class="emphasis"><em>target_module</em></span> as local rules. If either
          <span class="emphasis"><em>source_module</em></span> or <span class="emphasis"><em>target_module</em></span>
          is not supplied, it refers to the global module. <span class="emphasis"><em>source_rules</em></span>
          specifies which rules from the <span class="emphasis"><em>source_module</em></span> to import;
          <span class="emphasis"><em>target_rules</em></span> specifies the names to give those rules
          in <span class="emphasis"><em>target_module</em></span>. If <span class="emphasis"><em>source_rules</em></span>
          contains a name which doesn't correspond to a rule in <span class="emphasis"><em>source_module</em></span>,
          or if it contains a different number of items than <span class="emphasis"><em>target_rules</em></span>,
          an error is issued. For example,
        </p>
<pre class="programlisting"># import m1.rule1 into m2 as local rule m1-rule1.
IMPORT m1 : rule1 : m2 : m1-rule1 ;
# import all non-local rules from m1 into m2
IMPORT m1 : [ RULENAMES m1 ] : m2 : [ RULENAMES m1 ] ;
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="jam.language.modules.the__export__rule"></a><a class="link" href="language.html#jam.language.modules.the__export__rule" title="The EXPORT Rule">The <code class="literal">EXPORT</code>
        Rule</a>
</h4></div></div></div>
<p>
          <code class="literal">EXPORT</code> allows rule name aliasing across modules:
        </p>
<pre class="programlisting">rule EXPORT ( <span class="emphasis"><em>module</em></span> ? : <span class="emphasis"><em>rules</em></span> * )
</pre>
<p>
          The <code class="literal">EXPORT</code> rule marks <span class="emphasis"><em>rules</em></span> from
          the <code class="literal">source_module</code> as non-local (and thus exportable).
          If an element of <span class="emphasis"><em>rules</em></span> does not name a rule in <span class="emphasis"><em>module</em></span>,
          an error is issued. For example,
        </p>
<pre class="programlisting">module X {
  local rule r { ECHO X.r ; }
}
IMPORT X : r : : r ; # error - r is local in X
EXPORT X : r ;
IMPORT X : r : : r ; # OK.
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="jam.language.modules.the__caller_module__rule"></a><a class="link" href="language.html#jam.language.modules.the__caller_module__rule" title="The CALLER_MODULE Rule">The
        <code class="literal">CALLER_MODULE</code> Rule</a>
</h4></div></div></div>
<pre class="programlisting">rule CALLER_MODULE ( <span class="emphasis"><em>levels</em></span> ? )
</pre>
<p>
          <code class="literal">CALLER_MODULE</code> returns the name of the module scope enclosing
          the call to its caller (if levels is supplied, it is interpreted as an
          integer number of additional levels of call stack to traverse to locate
          the module). If the scope belongs to the global module, or if no such module
          exists, returns the empty list. For example, the following prints "{Y}
          {X}":
        </p>
<pre class="programlisting">module X {
    rule get-caller { return [ CALLER_MODULE ] ; }
    rule get-caller's-caller { return [ CALLER_MODULE 1 ] ; }
    rule call-Y { return Y.call-X2 ; }
}
module Y {
    rule call-X { return X.get-caller ; }
    rule call-X2 { return X.get-caller's-caller ; }
}
callers = [ X.get-caller ] [ Y.call-X ] [ X.call-Y ] ;
ECHO {$(callers)} ;
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="jam.language.modules.the__delete_module__rule"></a><a class="link" href="language.html#jam.language.modules.the__delete_module__rule" title="The DELETE_MODULE Rule">The
        <code class="literal">DELETE_MODULE</code> Rule</a>
</h4></div></div></div>
<pre class="programlisting">rule DELETE_MODULE ( <span class="emphasis"><em>module</em></span> ? )
</pre>
<p>
          <code class="literal">DELETE_MODULE</code> removes all of the variable bindings and
          otherwise-unreferenced rules from the given module (or the global module,
          if no module is supplied), and returns their memory to the system.
        </p>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
            Though it won't affect rules that are currently executing until they
            complete, <code class="literal">DELETE_MODULE</code> should be used with extreme
            care because it will wipe out any others and all variable (including
            locals in that module) immediately. Because of the way dynamic binding
            works, variables which are shadowed by locals will not be destroyed,
            so the results can be really unpredictable.
          </p></td></tr>
</table></div>
</div>
</div>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Rene Rivera, David Abrahams, Vladimir Prus<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div></td>
</tr></table>
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